Adding a node and then decommissioning the old node
You must prepare and start the replacement node, integrate it into the cluster, and then decommission the old node.
Be sure to use the same version of DataStax Enterprise on all nodes in the cluster, as described in the installation instructions.
Prepare and start the replacement node, as described in Adding nodes to an existing cluster.
If not using vnodes, see Adding single-token nodes to a cluster.
Confirm that the replacement node is alive:
Note the Host ID of the original node; it is used in the next step.
Using the Host ID of the original node, decommission the original node from the cluster using the nodetool decommission command.
Run nodetool cleanup on all the other nodes in the same datacenter.
Failure to run nodetool cleanup after adding a node may result in data inconsistencies including resurrection of previously deleted data.